Improve Temperature Uniformity Research Articles

An advanced modeling and experimental study to improve temperature uniformity of a solar receiver

Harnessing solar energy for thermochemical processing is an exciting and fast emerging research area with significant potential for reducing CO2 emissions. However, maintenance of a uniform temperature distribution as well as avoidance of hot spots in solar cavity receivers are challenges of present technology which are adversely affecting the process efficiency. This study presents a model based methodology as a design tool for iterative creation of optimum solar receiver geometry. Several discrete solutions are demonstrated as case studies via experimental testing of a solar receiver radiated by a 7 kW solar simulator. Experimental observations are compared with the results of the numerical analysis based on two-dimensional (2D) numerical model that couples the fluid flow and heat transfer mechanisms in the solar receiver. A Monte-Carlo ray tracing method was used to model the incoming radiation from the solar simulator and radiative exchange between the inner surfaces of the cavity receiver. Comparison of the simulation results to experimentally measured steady state temperatures at different points of the solar receiver shows 6.68% average absolute error confirming appreciable accuracy of the model. The results also show that reversing the gas flow direction and increasing the insulation layer do not improve the temperature distribution in the receiver. However, reducing the front flange dimensions and decreasing the inner receiver radius do enhance the temperature distribution and increase the average receiver temperature. Numerical results show that these changes can increase the average temperature of the inner cavity cylinder walls by 27%, and increase the temperature uniformity index by 58%. These findings provide essential insight for solar reactor design to reduce hot spot problems and improve temperature uniformity.

Development of an automated laser control system for improving temperature uniformity and controlling component strength in selective laser sintering

It has been shown that quality of components built using selective laser sintering (SLS) are strongly affected by the thermal history of the building process. Temperature variations of a few degrees across the powder surface can alter the mechanical properties of components and render them unsuitable for their intended purpose. Therefore, to improve the quality of SLS components and ease their adoption into the marketplace, temperature fluctuation issues must be addressed. Some success has been demonstrated in the past at reducing temperature non-uniformity by improving the heater system that pre-heats the polymer powder prior to sintering with the laser. This paper will cover a complimentary approach of actively controlling laser fluence on the powder surface based on infrared temperature measurements. By controlling the amount of energy input by the laser, a high level of control over the final part temperature can be achieved and uniformity can be improved. This paper will cover development of the feed-forward control system and will present results showing that for constant cross-section specimens, a 45% improvement in ultimate flexural strength standard deviation was achieved.

A Design Method to Improve Temperature Uniformity on Wafer for Rapid Thermal Processing

Single-wafer rapid thermal processing (RTP) is widely used in semiconductor manufacturing. Achieving temperature uniformity on silicon wafer is a major challenge in RTP control. In this work, a lamp configuration including five concentric lamp zones is designed to obtain uniform temperature distribution on the wafer. An optics-based model is developed to determine the optimal lamp design parameters, and a uniformity criterion is proposed to evaluate the effective irradiance distribution of the tungsten–halogen lamps on the wafer. This method can be used to determine geometric parameters of the lamp array in order to achieve uniform temperature distribution on the wafer. A realistic simulation of a cold wall RTP system with five lamp rings and a 200-mm wafer is performed. The proposed model makes way for a simple method for determining the optimal lamp design parameters in RTP systems.

Development and preliminary investigation of a modular chamber for calibration of relative humidity instruments

In the scope of the project HUMEA – Expansion of European research capabilities in humidity measurement within the EURAMET EMPIR program, the modular chamber for calibration of relative humidity instruments was designed, manufactured and characterized. The modular chamber consists of arbitrary numbers of aluminum blocks each of which provides accommodation for the one relative humidity probe and also has the fittings for pressure and temperature probes as well as ports for gas sampling and/or supplying. The gas can be supplied from the dew/frost point generator or the larger climatic chamber. In the latter case, the airflow through the chamber can be enhanced by using an additional fan. The preliminary study was carried out to investigate the improvement in temperature uniformity using a new chamber in combination with two climatic chambers. The investigation results show significant improvement in temperature uniformity thus lowering the uncertainties of the calibration of relative humidity instruments.

Experimental and numerical studies on air cooling and temperature uniformity in a battery pack

In this paper, a passive technique is examined by adding an inlet plenum to reduce the maximum temperature and improve temperature uniformity in a simple battery pack. The inlet plenum changes the direction of the flow and dramatically reduces the issues of air recirculation and dead-air regions between adjacent cells. The dimensions of the plenum and Reynolds number were optimized to enhance cooling and temperature uniformity at the cell and pack level. The results indicated that by increasing the Reynolds number to 7440, the maximum temperature decreased by 18.3% and the temperature uniformity increased 54.6%. However, there was no significant change in the maximum temperature and temperature uniformity beyond the Reynolds number of 7440. The developed battery pack achieved the desired temperature uniformity at the cell and pack level to less than 5°C.

Development and analysis of a technique to improve air-cooling and temperature uniformity in a battery pack for cylindrical batteries

In this paper, a passive approach to improve temperature uniformity in a simple battery pack, in which an inlet plenum is added as a secondary inlet to a battery pack with an axial air flow, is examined. This inlet plenum changes the direction of the flow and eliminates the problem of recirculation and non-availability of air between the adjacent cells. Three different configurations are considered to examine the effects of the orientation of inlet plenum and the cells. CFD (computational fluid dynamics) is used to perform detailed simulations of the battery packs and the results are validated with data obtained experimentally from one of the battery pack configuration. The thermal performance of the battery packs is compared to the baseline case, and the results indicate an average maximum temperature reduction of the cells by ∼4% and an improvement in temperature uniformity of the cells by ∼39%. This is a simple battery pack that uses forced air passive cooling (no moving parts required in the battery pack) and introduces mixing and turbulence in the air flow to increase the temperature uniformity in the battery pack.

Improving temperature uniformity of a lithium-ion battery by intermittent heating method in cold climate

The charge-discharge performances of lithium-ion batteries in hybrid electric vehicles (HEVs) and pure electric vehicles (EVs) decline rapidly at low temperatures. Many heating methods have been proposed to improve low-temperature performance, but these heating methods require long heating time and lithium-ion batteries at the end of heating have poor temperature uniformity. Recently, a self-heating lithium-ion battery (SHLB) has been proposed to recover charge-discharge performances of lithium-ion batteries at low temperature in short time. However, temperature uniformity of a lithium-ion battery heated by SHLB is also poor. A three-dimension heating finite element model is established in this work to analyze temperature gradient of a lithium-ion battery heated by SHLB heating method in detail, and intermittent SHLB heating method is proposed. For the intermittent SHLB heating method, a lithium-ion battery is heated for some time and stopped heating for some time instead of continuing heating. Through simulation analysis and comparison, heating for 0.1 s and stopping heating for 0.3 s is proposed to decrease the temperature gradient, and temperature difference is decreased from 10–11 K to 2–3 K.

A multi-pattern compensation method to ensure even temperaturein composite materials during microwave curing process

Microwave curing technologies have many advantages in manufacturing fiber reinforced polymer composite materials used in aerospace products, compared with traditional autoclave curing technologies. However, the uneven electromagnetic field of microwave in the cavity of the curing chamber results in uneven temperature on the surface of composite laminates during curing, which has been a major obstacle in industrial applications worldwide. Existing methods attempted to solve the problem by the random superposition of uneven electromagnetic fields, but the results were still not satisfactory to meet the high quality requirements of aerospace parts. This paper reveals the one-to-one correspondence between heating patterns of composite parts and microwave curing system settings, and reports a new concept to solve this problem by continuously monitoring and compensating the uneven temperature distribution in real-time. Experimental results from both fiber optical fluorescence sensors and infrared thermal imagers showed significant improvement in temperature uniformity compared with existing methods.

A multi-pattern compensation method to ensure even temperature in composite materials during microwave curing process

Microwave curing technologies have many advantages in manufacturing fiber reinforced polymer composite materials used in aerospace products, compared with traditional autoclave curing technologies. However, the uneven electromagnetic field of microwave in the cavity of the curing chamber results in uneven temperature on the surface of composite laminates during curing, which has been a major obstacle in industrial applications worldwide. Existing methods attempted to solve the problem by the random superposition of uneven electromagnetic fields, but the results were still not satisfactory to meet the high quality requirements of aerospace parts. This paper reveals the one-to-one correspondence between heating patterns of composite parts and microwave curing system settings, and reports a new concept to solve this problem by continuously monitoring and compensating the uneven temperature distribution in real-time. Experimental results from both fiber optical fluorescencesensors and infrared thermal imagers showed significant improvement in temperature uniformity compared with existing methods.

Improvement of temperature uniformity in microchannel with pin-fin based on endwall fillet structure

Energy and mass transfer process are involved in many industries, such as energy, transportation, aeronautics and astronautics, electronic, manufacturing, among which, the heat exchanger plays a very key role. With the development of science and technology and the increasing requirements for energy conservation and emission reduction, the efficiency of heat exchange system has to be promoted to meet the demand of higher heat intensity and thermal load. The high-efficient and energy-saving compact heat exchanger such as microchannel heat sink has gained more attractions in academic researches and engineering applications. Microchannel with pin-fin is widely used in engineering applications due to its high efficiency in heat and mass transfer, but the high temperature region formed in the rear of the cylinder and the non-uniformity temperature field increase the temperature gradient and generate extra thermal spreading resistance, which would, to a large extend, influence the regulation of the system and the economy and reliability of the equipments. Therefore, the endwall fillet structure is proposed in this work, based on researches about the performance of CDA (controlled diffusion airfoil) blade with fillet, to improve the temperature uniformity and heat transfer performance of microchannel with pin-fin. The periodical laminar flow and heat transfer performances are comparatively studied. The results show that the flow resistance coefficient f of the microchannel with filleted pin-fin does not increase significantly compared to traditional pin-fined microchannel, which means the introducing of the fillet will enhance the heat transfer while f of the microchannel is almost a constant. The maximum increase of f is only 2.03%. Moreover, two separate symmetrical secondary flows develop in microchannel with smooth cylinder, with one on the top of the other. After adding the proposed structures, at low Reynolds number, the lower span-wise secondary flow is enhanced as the radius increases and these two span-wise secondary flows gradually merge into one which develops along the normal direction. At high Reynolds number, the mainstream low-temperature core region is obvious asymmetry: it moves downwards gradually as Reynolds number increases. Besides, at low Reynolds number (0–120), the fillet improves the heat and mass transfer between the main stream core and areas near the wall, enhances the thermal uniformity of the pin-fin and heated walls, improves the heat transfer performance of the rear of the cylinder and eliminates the high temperature area in the pin-fin. And local high-temperature region on the top half of the microchannel decreases, which contributes to the extension of low-temperature region and the decrease of average temperature. As the radius of the fillet increases, the effects mentioned above are gradually enhanced. The heat transfer coefficient of the channel reaches a maximum augmentation of 16.93%, and the flow resistance coefficient of the microchannel with filleted pin-fin does not increase significantly. Comparing with the synthetical thermal performance coefficient of pin-fined microchannel heat sink, that of the proposed filleted pin-fin microchannel increases 16.22% at most. As the Reynolds number increases, the influence of the fillet structure decreases. The study motivation of combining separation flow researches of rotatory machines with heat transfer enhancement, as well as the resulting design are a beneficial attempt for scientific research and engineering application.

Experimental study of a passive thermal management system using copper foam-paraffin composite for lithium ion batteries

A passive thermal management system using copper metal foam saturated with phase change materials is designed for LiFePO4 battery pack. Copper metal foam is aimed to enhance low thermal conductivity of PCM and improve temperature uniformity of the battery pack. The thermal efficiency of the system is experimentally investigated and compared with two dissipation patterns of air cooling and pure PCM. The results show that the dissipation pattern of the foam-PCM composite can significantly reduce the battery’s surface temperature compared with the other two patterns. Moreover, the foam-PCM composite can bring the battery pack a better temperature uniformity, especially during the higher discharge rate.

Numerical Research on Magnetic Field, Temperature Field and Flow Field During Melting and Directionally Solidifying TiAl Alloys by Electromagnetic Cold Crucible

The electromagnetic cold crucible (EMCC) technique is an effective method to melt and directionally solidify reactive and high-temperature materials without contamination. The temperature field and fluid flow induced by the electromagnetic field are very important for melting and controlling the microstructure. In this article, a 3D EMCC model for calculating the magnetic field in the charges (TiAl alloys) using the T-Ω finite element method was established and verified. Magnetic fields in the charge under different electrical parameters, positions and dimensions of the charge were calculated and analyzed. The calculated results show that the magnetic field concentrates in the skin layer, and the magnetic flux density (B) increases with increasing of the frequency, charge diameter and current. The maximum B in the charge is affected by the position of the charge in EMCC (h 1) and the charge height (h 2), which emerges at the middle of coils (h c) when the relationship of h c < h 1 + h 2 < h c + δ is satisfied. Lower frequency and smaller charge diameter can improve the uniformity of the magnetic field in the charge. Consequently, the induced uniform electromagnetic stirring weakens the turbulence and improves temperature uniformity in the vicinity of the solid/liquid (S/L) interface, which is beneficial to forming a planar S/L interface during directional solidification. Based on the above conclusions, the TiAlNb alloy was successfully melted with lower power consumption and directionally solidified by the square EMCC.

Thermal performance of liquid cooling based thermal management system for cylindrical lithium-ion battery module with variable contact surface

In this paper, a novel liquid cooling based thermal management system for the cylindrical lithium-ion battery module with variable contact surface is designed. Contact surface size is determined by aluminum block length. The cooling system relies on aluminum block which can effectively transfer heat from battery to cooling water. A battery module with six cells along flow channel is chosen to study the effects of aluminum block length and velocity on the thermal performance in the way of simulation. Three change types of contact surface are studied and their performance are compared with the system with constant contact surface at different inlet velocities. The results indicated that the system with variable contact surface is superior to the system with constant contact surface. It can significantly improve temperature uniformity. When inlet velocity is 0.05m/s, the maximum temperature can decrease to the same value and temperature difference decreases by 6%, 14% and 28%. Finally, an optimal design is presented with system weight, pump power consumption and cooling performance taken into consideration.

General Characterization of Jet Impingement Array Heat Sinks With Interspersed Fluid Extraction Ports for Uniform High-Flux Cooling

In conventional jet impingement array heat sinks, all the spent coolant is extracted from component edges, resulting in cross-flow interference and nonuniform heat transfer. Jet impingement arrays with interspersed fluid extraction ports can reduce cross-flow, improving heat transfer uniformity and reducing pumping loads. While this configuration offers technical advantages, limited pressure drop and heat transfer data are available. In this investigation, simulations are performed for laminar single-phase jet impingement arrays with interspersed fluid extraction ports over varying flow rates (Rej = 20–500), fluid transport properties (Pr = 1–100), and geometries (jet pitch to diameter ratios of 1.8–7.1 and jet diameter to gap height ratios of 0.1–4.0). The simulation approach is validated for isolated jet impingement, and grid sensitivity studies are performed to quantify numerical uncertainty. Over 1000 randomized cases are evaluated to develop new correlations for Nusselt number and pressure-drop k-factors. Conjugate heat transfer studies are performed to compare heat sinks (5 × 5 mm heated, 500 W m−2 heat flux) employing jet arrays with interspersed fluid extraction ports, microchannels, and jet arrays with edge fluid extraction. The design with jet arrays with interspersed fluid extraction ports yields lower average temperatures, improved temperature uniformity, and modest pressure drops. This study provides new data for jet impingement thermal management and highlights the technical potential of configurations with interspersed fluid extraction ports.

Effects of Arrangement and Phase Difference of Oscillation of Synthetic Jets on Heat Transfer in Micro-channels

In this study, effects of two different arrangements and π-radian phase difference in the oscillation of membranes of three synthetic jets, in a cross-flow of a micro-channel, on heat transfer and temperature distribution uniformity of a hot wall, located at certain distance from the synthetic jet outlet, were numerically studied by a three-dimensional model using dynamic mesh. Obtained results show that synthetic jets provide better cooling for the hot plate; however, the position and phase difference of the oscillation in the actuators of the synthetic jets are effective on the degree of cooling improvement. Depending on the position and operating conditions of the synthetic jets, reduction in the average temperature of the hot plate and increase in the Nusselt number vary from 21% to 28% and from 64% to 92% as compared to micro-channel without synthetic jet, respectively. In addition, operation of the synthetic jets improved temperature uniformity over the hot wall and improvement varies from 34% to 47% as compared to case of no synthetic jet in the micro-channel.DOI: http://dx.doi.org/10.5755/j01.mech.23.1.14091

Analysis of nozzle gas speed on the performance of the zoned and staged gas-fired radiant tube

In this study, the nozzle characteristics of zoned and staged double P-type gas-fired radiant tube were improved to optimize combustion efficiency. A three-dimensional finite element model was established, and a grid-independence study was conducted to guarantee the accuracy of the calculation results. Corresponding experiments were designed to prove the reliability and accuracy of the simulation model. Then, the developed mode was used to determine the flow field characteristics of the zoned and staged gas-fired radiant tube. Moreover, the gas and wall temperatures were calculated by altering the gas speeds in the main and branch tube nozzles respectively. The effects of nozzle gas speed on the radiant tube were compared. Results showed that increasing the air speed of the main tube nozzle could decrease the maximum temperature and the wall temperature difference, improve temperature uniformity, and slightly increase thermal efficiency. Increasing the air speed of the branch tube nozzle could reduce the maximum wall temperature and enhance surface temperature uniformity; but these effects were relatively not significant.

Studying heat transfer on inclined printed circuit boards during vapour phase soldering

PurposeThe paper aims to present an investigation of heating during vapour phase soldering (VPS) on inclined printed circuit board (PCB) substrates. The PCB is a horizontal rectangular plate from the aspect of filmwise condensation with a given inclination setting.Design/methodology/approachThe paper focuses on the measurement of temperature distribution on the PCBs with a novel setup immersed in the saturated vapour space. The measuring instrumentation is optimized to avoid and minimize vapour perturbing effects.FindingsThe inhomogeneity of the heating is presented according to the lateral dimensions of the PCB. The inclination improves temperature uniformity, improves heat transfer efficiency; however, a minor misalignment may affect the flow and result in uneven heating.Practical implicationsThe results can be implemented for practical improvements in industrial ovens with the use of intended inclination. The improvements may consequently point to more efficient production and better joint quality.Originality/valueThe novel method can be used for deeper investigation of inclination during and can be complemented with numerical calculations. The results highlight the importance of precise PCB holding instrumentation in VPS ovens.

Modeling and simulation of furnace pulse firing improvements using fuzzy control

Pulse firing offers significant process and productivity benefits, such as improved temperature uniformity and high heat transfer rates to the product load through maximum system turndown and utilizes the system’s burners at their most efficient firing rates. However, overshoot and undershoot is unavoidable. To minimize these effects, the system operates the burner at an enhanced turndown rate. Faster cycle rates improve temperature uniformity but reduce equipment lifetime. Therefore, a tradeoff exists between furnace temperature uniformity and the cycle rate used by the pulse firing control. This paper proposes models and simulates an advanced technique that improves temperature uniformity while decreasing the cycle time used by the pulse firing control. This provides reliable, safe furnace operating conditions, thereby extending the lifetime of the equipment. After an analysis of a furnace’s combustion system that utilizes the pulse firing method to control the heat demand of the furnace, non-linearities were found in the combustion system. To improve the performance of the temperature control, an error-driven function was coupled to the control strategy to compensate the signal error fed to a proportional–integral–derivative controller. The error-driven function was implemented using a fuzzy system, which improved the temperature uniformity and allowed a 60% duty cycle reduction in comparison with similar combustion systems.

Laminar forced convection heat transfer from laterally perforated-finned heat sinks

Thermal and hydraulic performance of laterally perforated-finned heat sinks (LA-PFHSs) operating in the laminar flow regime were experimentally investigated and compared to that of the solid-finned heat sink (SFHS). Square cross sectional perforations at three different sizes were distributed equidistantly along the length of the LA-PFHSs. For each perforation size, five different porosities were tested. Locally measured thermal resistances at various locations along the heat sink were acquired. The results signify the key roles of geometrical parameters, mainly the fin pitches, on thermal-fluid characteristics of LA-PFHSs. The effects of both perforation size and porosity on overall pressure drops were also measured and presented. LA-PFHSs increased the pressure drops due to cavities formed over the perforations. The pressure drag was found to be the dominant pressure drop when compared with friction drag. However, the pressure drops became independent of the porosity beyond a threshold perforation size. Overall, LA-PFHSs are promising thermal management solutions to decrease thermal resistance and improve temperature uniformity across the heat sink base at a given pumping power, if the optimum range of porosity is obtained for a given perforation size. The results indicate that weight sensitive applications would be the most promising use for LA-PFHS. A new parameter as the mass-based thermal resistance was defined, and for the cases studied in this paper, over 45% reduction in the mass-based thermal resistance of the SFHS was achieved using LA-PFHSs with the maximum porosity.

Combining a distributed flow manifold and 3D woven metallic lattices to enhance fluidic and thermal properties for heat transfer applications

The fluidic and heat transfer capabilities of 3D woven lattice materials were reported recently under axial and bifurcated flow patterns, but three critical performance indices – pressure drop, average surface temperature and temperature uniformity – could not be optimized simultaneously using these flow patterns. Here we combine the 3D weaves with manifolds to create a novel 3D flow pattern that enhances temperature uniformity, while also maintaining low pressure drops and surface temperatures. These three properties were characterized at room temperature for a range of flow rates using water as the working fluid. Three different weaves thicknesses were investigated: 12.7mm, 6.4mm, and 3.2mm, with manifold thicknesses of 12.7mm, 19.0mm, and 22.2mm, respectively, to provide a constant, combined weave-manifold thickness of 25.4mm. The properties of this new weave/manifold system are compared to those obtained using just the manifold (with no weave) and just the weave (with no manifold). Comparisons show that the addition of the weave lowers the average substrate temperature and temperature variations significantly, although pressure drop is increased. They also show that the addition of the manifold improves temperature uniformity significantly, and also lowers the average substrate temperature and the pressure drop. No specific ratio of weave to manifold thickness was found to be superior in all of the performance indices. The thermal performances are then evaluated at different pumping powers: the weave/manifold system and its distributed array flow pattern prevail. Finite element simulations were performed on a reduced and simplified model to explain the observed experimental trends, and manifold opening patterns were manipulated to demonstrate further potential property enhancements. The multiple benefits of this manifold system can be extended to common heat exchanger media beyond weaves.